What had proven true in the time of Pizarro, San Martin, and Santa Cruz, was still true--the successful invasion or defence of Peru depended on the control of the Pacific. Whichever power should obtain a naval preponderance would surely get the nitrate territory--a rainless, cropless region where an army must be sustained by supplies brought by sea--and then could attack the other at its capital. Chile had two new iron-clads, the _Cochrane_ and the _Blanco_, besides two good cruisers and several gunboats. The two Peruvian iron-clads, the _Huascar_ and the _Independencia_, were older, though their speed was superior. The Chileans opened the war on the ocean by blockading the Peruvian ports in the extreme south, but Miguel Grau, the able seaman and intrepid fighter who commanded the Peruvian fleet, at once attacked the Chilean cruisers which were lying off Iquique. The _Huascar_ rammed and sank the _Esmeralda_, but while his other iron-clad was pursuing the _Covadonga_, she ran upon the rocks and was lost. This was in reality a deathblow to Peru, but the gallant Grau devotedly determined to see what his single ship, rapidly manoeuvred, could do to make unsafe the embarkation of a Chilean army. For four months he terrorised the coast from Antofagasta to Valparaiso. Chile could not take a step until she had disposed of Grau and his dreaded _Huascar_. The blockade of Iquique was abandoned as useless; the iron-clads ordered back to Valparaiso to be cleaned and repaired so that they might match the _Huascar_ in speed; new officers were put in command; and on October the first the Chilean fleet set sail from Valparaiso on a systematic chase for the Peruvian iron-clad. On reaching Antofagasta it was divided into two squadrons, the _Cochrane_ leading one and the _Blanco_ the other, and they immediately began patrolling the coast.